Trademarks are hereinafter shown in upper case.
The name “potassium monopersulfate” is commonly used in the trade, and is used hereinafter to refer to the mixed triple salt 2KHSO5.KHSO4.K2SO4, a crystalline salt of enhanced solid-state stability. In the treatment of recirculating water systems, especially in swimming pools, spas and hot tubs, potassium monopersulfate is an effective non-chlorine oxidizer for the reduction of non-microbial, organic contaminants which make water dull and cloudy and reduce chlorine sanitizer efficiency. Various active halogen agents which dissolve in water to provide free available halogen are well-known in the art and are used as sanitizing agents to control microbial and algal growth in recirculating water systems.
Martin, in U.S. Pat. No. 6,409,926, uses the separate addition of a halogen donor source (including sodium dichloroisocyanurate), a coagulating agent, and a peroxygen compound (including potassium monopersulfate) for the removal of volatile halogenated compounds from the air and water in an indoor aquatic facility. Martin does not describe compositions comprising premixed potassium monopersulfate and an active halogen agent.
In general, commercial suppliers strongly recommend that chemicals providing a source of active oxygen should not be mixed with active halogen sources or precursors thereof. Many such mixtures are chemically unstable as solid mixtures, and are capable of exothermic reactions with the evolution of poisonous halogen gas. For example, the following recommendations are made:
The MSDS of PPG for Calcium Hypochlorite Granular (Date Jun. 15, 1998) states:                “DANGER! Strong Oxidizing Agent! Mix only with water. Contamination may cause fire or explosion. Do not add this product to any dispensing device containing remnants of any other product” [emphasis added].        
The Clinfax MSDS for CLINIFAX Bleach Tablets (sodium dichloro-s-triazinetrione dihydrate, date July 1998) states:                “Substances to be avoided (incompatible substances): Organic substances, oils, fat, saw dust, reducing agents, nitrogen-containing compounds, sodium hypochlorite, calcium hypochlorite, other oxidizing agents, acids and alkaline substances” [emphasis added].        
The MSDS of the U.S. Department of Transportation, 49 CFR, for Microphor Chlorinating Slugs (trichloroisocyanuric acid), Revised Jun. 22, 2000 states:                “Incompatibility: Organic materials, reducing agents, nitrogen-containing materials,        other oxidizers, acids, bases, oils, grease, sawdust, dry fire extinguishers containing monoammonium compounds” [emphasis added].        
The OXONE monopersulfate compound technical information bulletin P-200838 (4/2000), from E. I. du Pont de Nemours and Company, lists the following materials as “incompatible” and which should not be transported or stored in proximity to OXONE:                “Compounds containing halides or active halogens. OXONE can oxidize halides to active halogens (for example chloride to chlorine), and the acidity of OXONE might react with an active halogen compound to release halogen gas”        
Generally, if potassium monopersulfate is combined with alkali and alkaline earth hypochlorites, the mixture is not stable. Such mixtures are unsafe for the end-user because, when contacted with water, poisonous chlorine gas is evolved immediately due to the acidic nature of potassium monopersulfate and the high solubility and reactivity of the hypochlorite salt in water. Furthermore, such mixtures are not stable because the reactivity of hypochlorite salts and potassium monopersulfate is very exothermic and can cause fires or explosions.
It is therefore desirable to have a safe, stable combination of potassium monopersulfate with an active halogen agent in a single composition that provides the dual action of peroxygen oxidation and the establishment or maintenance of a free halogen residual to control microbial and algal growth. Such a composition would be useful in the treatment of recirculating water systems, such as in various types of recreational, ornamental and industrial water systems. The present invention provides safe and stable compositions which comprise mixtures of potassium monopersulfate and suitable active halogen agents.